1 files changed, 4 insertions, 0 deletions
diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index b51d644bdc..73635cf456 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -1559,6 +1559,10 @@ openStatsFile (char *filename,           // filename, or NULL
         if (*filename != '\0') {  /* stats file specified */
             f = fopen(filename,"w");
         } else {
+            if (filename_fmt == NULL) {
+                errorBelch("Invalid stats filename format (NULL)\n");
+                return -1;
+            }
             /* default <program>.<ext> */
             char stats_filename[STATS_FILENAME_MAXLEN];
             sprintf(stats_filename, filename_fmt, prog_name);